1. Field of the Invention
The present invention relates generally to methods for synthesizing linear macromolecular structures, such as substituted and unsubstituted polyolefin or polymethylene. More particularly, the present invention involves a method which allows one to accurately control polymerization so that linear oligomers and polymers having pre-selected carbon chain lengths can be synthesized. The present invention also relates to methods for synthesizing highly functionalized polymers and block copolymers. Further, the present invention involves the synthesis of polymers having a high degree of mono-dispersity.
2. Description of the Related Art
Linear polymers, such as polyethylene and poly(methylmethacrylate), are commonly formed by polymerization of their respective ethylene and methylmethacrylate monomers. The general polymerization reactions for these two polymers are set forth in equations A and B. ##STR1##
The above polymerization reactions are typically catalyzed with a catalyst such as a Ziegler-Natta catalyst. These polymerization reactions are also commonly initiated with a free radical, nucleophile or electrophile. The existing catalyzed or free radical polymerization reactions are capable of producing oligomers and polymers having chain lengths where n ranges from 50 to hundreds of thousands.
One problem with the present polymerization procedures is that it is difficult to accurately control the length of the polymer chain that is produced during the polymerization reaction. The chain length of the polymer may be controlled somewhat by varying reaction conditions. However, the reaction mechanisms inherent in catalyzed or free radical initiated polymerization reactions makes it extremely difficult to achieve more than qualitative control over the molecular weight, i.e., chain length, of the resulting polymer.
The polymer products produced by the above conventional polymerization reactions tend to include individual polymers which vary widely in chain length. In many situations it is desirable to have a polymer product with this high degree of dispersity. However, there are also many instances where it would be desirable to produce a polymer product which has a low degree of dispersity with respect to polymer chain length. Such polymer products having relatively uniform polymer molecular weight are useful in applications, such as optic devices, and any application where control of molecular weight and functionality is important.
Another problem with existing polymerization procedures is that highly functionalized polymers are difficult or impossible to prepare. For example, polymerization of many 1,2-disubstituted olefins is unknown or difficult. Stilbene and dimethyl fumarate are examples of two disubstituted olefin monomers which are difficult to polymerize using conventional catalytic or free radical polymerization protocols.
In view of the above problems with conventional polymerization procedures, there is a continuing need to develop new approaches for synthesizing polymers where chain length can be accurately controlled and the polydispersity of the resulting polymer product minimized. In addition to these goals, it would also advantageous if the new polymer synthesis procedure could also be used to synthesize highly functionalized polymers.
In many instances it is desirable to add a single carbon atom to an existing carbon atom or chain. One procedure which has been used to add single carbon atoms to a carbon chain is based upon homologation technology. Tefariello et al. (J. Am. Chem. Soc. 88:4757,1966) discloses an example of a homologation process in which a single carbon atom is added to an alkyl group of an alkyl borane by reaction with a ylid by reacting the ylid with a trialkyl borane. An important requirement for this type of homologation procedure is that the reaction conditions be carefully controlled to prevent multiple homologation. In general, these homologation processes are carried out at temperatures of around 0.degree. C. and include equal molar amounts of the ylid and trialkyl borane in order to prevent multiple homologation reactions from occurring.